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Earth Science Activities
That Sinking Feeling Materials:
Background: Calcium carbonate is a compound that is carried in solution in ocean water. When the calcium carbonate precipitates out of solution as calcite, many crystals grow together and form the chemical sedimentary rock known as limestone. Limestone may also contain other minerals and sediments, but it is comprised of at least 50 percent calcite. Limestone is usually deposited on sea or ocean floors. Large areas of the United States, including Florida, are underlain by limestone because oceans once covered much of the country for millions of years. This is significant because limestone is subject to
chemical weathering, resulting in rock changes. Water is an
important agent of chemical weathering. When the hydrogen and oxygen
atoms in water mix with carbon dioxide molecules in the air, a weak acid,
known as carbonic acid, reacts with minerals such as calcite, the main
mineral in limestone. The product of this reaction then dissolves
and can be carried away. Over thousands of years, carbonic acid has
weathered enough limestone to create caves. Inside the caves, water
often drips slowly from cracks in the cave walls and ceilings. If
enough water seeps through, it can eventually dissolve the underground
rock. If the rock is dissolved near the surface, a sinkhole may
form. A sinkhole is a depression that forms when the roof of a cave
collapses. Development of groundwater resources for municipal,
industrial and agricultural water supplies creates regional groundwater
level declines. The decline of available groundwater plays a role in
accelerating sinkhole formation, thereby increasing susceptibility of the
aquifers to contamination from surface water drainage. Increased sinkhole development and property loss are strongly correlated to human activity and cultural development. There are several reasons for this correlation. First, the rapid growth and development makes it more likely that new sinkholes will be reported, and the construction of roads and industrial or residential buildings increases exposures to the rise of property damage. Second, Land-use changes in rapidly developing areas are often loosely controlled and include altered drainage, new collection areas for surface water, and new construction in sinkhole-prone areas. Finally, the changing land use is often associated with population increases and increasing demands for water supplies, which leads to the lowering of regional ground-water levels, risking salt water intrusion and increases run-off, diminishing water quality, which only accelerates the calcium carbonate dissolution process. Procedure: 1. Have students access the USGS - Earthshots: Orlando Change webpage. Have them toggle through the images available from varying years. It might be helpful for some students to print the images or have printed images available to them for analysis. 2. Ask the students if they notice any significant changes to the area in the satellite imagery. Ask the students if they are aware of any man-made changes to the area over the years that the images were captured. Might there be any correlations? 3. Ask the students or have them research the topic of sinkholes. What does a sinkhole have to do with water? Do the recent man-made developed areas and need for water correlate with the increase of sinkholes? 4. From the satellite imagery, have the students estimate approximately how many karstic lakes have been created over the past 20 years. What impact will these lakes have on local water quality? Assessment:
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